# Copyright 1999-2020 Alibaba Group Holding Ltd.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


import pandas as pd
import numpy as np

from ... import opcodes as OperandDef
from ...core import OutputType
from ...serialize import StringField
from ...tensor.core import TensorOrder
from ...utils import lazy_import
from .core import DataFrameReductionOperand, DataFrameReductionMixin


cudf = lazy_import('cudf', globals=globals())


class DataFrameUnique(DataFrameReductionOperand, DataFrameReductionMixin):
    _op_type_ = OperandDef.UNIQUE
    _func_name = 'unique'

    _method = StringField('method')

    def __init__(self, method=None, **kw):
        super().__init__(_method=method, **kw)

    @property
    def method(self):
        return self._method

    @classmethod
    def tile(cls, op):
        if op.method == 'tree':
            return super().tile(op)
        else:
            raise NotImplementedError("Method {} hasn't been supported".format(op.method))

    @classmethod
    def _execute_map(cls, ctx, op):
        xdf = cudf if op.gpu else pd
        in_data = ctx[op.inputs[0].key]
        try:
            uniques = xdf.unique(in_data)
        except AttributeError:   # pragma: no cover
            # for cudf
            uniques = in_data.unique()
        # convert to series data
        ctx[op.outputs[0].key] = xdf.Series(uniques)

    @classmethod
    def _execute_combine(cls, ctx, op):
        xdf = cudf if op.gpu else pd
        in_data = ctx[op.inputs[0].key]

        # convert to series data
        ctx[op.outputs[0].key] = xdf.Series(in_data.unique())

    @classmethod
    def _execute_agg(cls, ctx, op):
        in_data = ctx[op.inputs[0].key]
        ctx[op.outputs[0].key] = in_data.unique()

    def __call__(self, a):
        self.output_types = [OutputType.tensor]
        return self.new_tileables([a], shape=(np.nan,), dtype=a.dtype, order=TensorOrder.C_ORDER)[0]


def unique(values, method='tree'):
    """
    Uniques are returned in order of appearance. This does NOT sort.

    Parameters
    ----------
    values : 1d array-like
    method : 'shuffle' or 'tree', 'tree' method provide a better performance, 'shuffle'
    is recommended if the number of unique values is very large.
    See Also
    --------
    Index.unique
    Series.unique

    Examples
    --------
    >>> import mars.dataframe as md
    >>> import pandas as pd
    >>> md.unique(md.Series([2, 1, 3, 3])).execute()
    array([2, 1, 3])

    >>> md.unique(md.Series([2] + [1] * 5)).execute()
    array([2, 1])

    >>> md.unique(md.Series([pd.Timestamp('20160101'),
    ...                     pd.Timestamp('20160101')])).execute()
    array(['2016-01-01T00:00:00.000000000'], dtype='datetime64[ns]')

    >>> md.unique(md.Series([pd.Timestamp('20160101', tz='US/Eastern'),
    ...                      pd.Timestamp('20160101', tz='US/Eastern')])).execute()
    array([Timestamp('2016-01-01 00:00:00-0500', tz='US/Eastern')],
          dtype=object)
    """
    op = DataFrameUnique(method=method)
    return op(values)
